Waits for an element to become visible on a page (by default waits for 1sec).
Element can be located by CSS or XPath.

```js
I.waitForVisible('#popup');
```

@param {CodeceptJS.LocatorOrString} locator element located by CSS|XPath|strict locator.
@param {number} [sec=1] (optional, `1` by default) time in seconds to wait
@returns {void} automatically synchronized promise through #recorder
